1. Field of the Invention
The present invention relates to a wire bonder which performs assembly of semiconductor integrated circuits (IC), etc., and more particularly, relates to a wire bonder which is able to easily detect the amount of movement of the end of a bonding tool of a bonding head thereof as well as the position of said bonding tool.
2. Description of the Prior Art
With respect to the prior art, in the case of manufacturing semiconductor integrated circuits (IC) or large-scale integrated circuits (LSI), by displacing a bonding tool holding a wire with respect to a lead frame and semiconductor pellet after positioning said lead frame on which said semiconductor pellet is arranged on a conveyor device, bonding is performed by respectively guiding the wire to a lead arranged on said lead frame and to a pad on said semiconductor pellet. Wire bonding by this type of process is performed using bonding head 1 possessing an oscillation mechanism which allows oscillation of bonding tool 2 in the vertical direction as indicated in FIGS. 1(A) and 1(B).
The following provides a description of the composition of said bonding head 1.
In FIG. 1(A) and 1(B), bonding arm 3 is mounted on shaft 5 supported by head base 4 so as to be allowed to oscillate. Horn 3a is mounted on bonding arm 3 and is formed into an approximately conical shape which tapers towards the free end. Bonding tool 2 (also referred to as a capillary) is mounted on the end of said horn 3a. A hole is formed in the center of said bonding tool 2 which allows the insertion of wire 11 made of aluminum, gold or other wire material. The device is composed so as to allow said wire 11, which is clamped by a clamper or similar device (not shown) at the top of horn 3a, to be fed out a fixed length at a time from the end of bonding tool 2 through said hole. The other end of said wire 11 is wound around a reel (not shown) so that a fixed amount of tension is applied to prevent slack from forming in said wire 11.
In addition, voice coil 6a of a linear motor 6 is provided on the other end of above-mentioned bonding arm 3. This coil 6a is inserted within a magnetic cap of magnetic circuit 6b, comprised of a permanent magnet and a yoke, so as to be allowed to oscillate vertically. This magnetic circuit 6b is fixed to head base 4. This head base 4 is fixed on an XY table (not shown) which can be driven in the X and Y directions. In addition, the end of shaft 5 which supports bonding arm 3 is coupled with shaft 8a of rotary encoder 8 mounted on head base 4 by means of coupling 7.
On the other hand, a semiconductor pellet (not shown), which is positioned and arranged on a bonding stage on which bonding work is performed, is placed beneath bonding tool 2. In addition, a detecting sensor (not shown) is provided on the side of bonding arm 3 which is comprised of an optical sensor or similar device that detects the reference position (origin) of bonding arm 3.
The following provides a description of the operation of the device having the composition described above.
When coil 6a of linear motor 6 mounted on bonding arm 3 is excited, bonding arm 3 rotates while oscillating in the counter-clockwise direction as viewed in FIG. 1(A) using shaft 5 as a pivot point as a result of the thrust of linear motor 6. Then, after the end of bonding tool 2 has been lowered at high speed to a specified position above a pad of a semiconductor pellet, the speed of bonding tool 2 is reduced to low speed. Bonding tool 2 then crushes a ball formed on the end of wire by means of a torch (an electric discharge device) (not shown) located on the end of said bonding tool 2, onto the upper surface of the pad on the semiconductor pellet, thus resulting in thermocompression bonding. Bonding is often aided at this time by applying ultrasonic vibration to the end of bonding tool 2.
The amount of movement of said bonding tool 2 is calculated by a control device not shown, such as a microcomputer or similar device, by counting a series of pulses output from rotary encoder 8 according to the angle of rotation traversed.
Conversely, following bonding, bonding arm 3 is rotated about shaft 5 in the clockwise direction as viewed in FIG. 1(A) by a previously set amount by exciting coil 6a of linear motor 6, after which it is stopped at that position. Bonding is then performed by moving bonding head 1 to the lead side, which is the next bonding point, according to the same process as described above, by moving the XY table.
The above-mentioned process is repeated until all pads of the semiconductor pellet and all leads of the lead frame are connected to complete bonding.
However, in the case of the wire bonder of the prior art, as the amount of movement of bonding arm 3 is determined by a control device by counting a series of pulses output from rotary encoder 8, this wire bonder has the disadvantage of not being able to determine the absolute amount of movement of bonding arm 3 based on the output of rotary encoder 8 alone. In other words, although the number of pulses can be counted to allow determination of the amount of movement corresponding to that number of pulses, the device is not able to confirm the location where the end of bonding tool 2 is positioned. Consequently, a separate detection sensor, which detects the origin position that serves as the reference for the end of bonding tool 2, is required. In addition, since the wire bonder of the prior art is dependent upon the efficiency of the resolution of the series of pulses that are output from rotary encoder 8, it also has the disadvantage of it being difficult to accommodate the entire amount of movement of bonding arm 3 from high speed to low speed with the resolution of rotary encoder 8. Moreover, as rotary shaft 8a of rotary encoder 8 is linked in a fixed fashion to shaft 5 by means of coupling 7, the wire bonder of the prior art also has the disadvantage of requiring considerable time for assembly and adjustment in order to align the shaft centers of the above-mentioned shafts since smooth oscillating method of bonding arm 3 cannot be obtained unless said shaft centers are aligned accurately.